Examples of the currently-used printing apparatus of this type include a printer provided with printing heads, first and second guide rollers, a rotary encoder, and a drive roller (see, for example, Japanese Unexamined Patent Publication 2010-158814).
In the printer, the first guide roller, the second guide roller, and the drive roller are disposed in this order from upstream on a transportation path for web paper, and the printing heads are disposed between the first and second guide rollers. Here, printing is performed while discharge timings of ink droplets from the printing heads are controlled in accordance with a transportation speed of the web paper.
The transportation speed of the web paper and the discharge timings of the ink droplets from the inkjet heads influence printing quality. Accordingly, the transportation speed of the web paper is determined by detecting a number of rotations of the second guide roller downstream of the printing heads with a rotary encoder, and the discharge timings from the printing heads are each adjusted based on the transportation speed. This allows accurate detection of change in transportation speed adjacent to the printing heads and thus allows adjustment of the discharge timings of the ink droplets. This achieves suppression of misregister caused by the variation in transportation speed, leading to enhanced printing quality.
However, the example of the currently-used apparatus with such a construction has the following drawback.
That is, the currently-used apparatus performs printing based on indirect information from the rotary encoder although the discharge timings of the ink droplets are adjusted based on the transportation speed of the web paper. As a result, misregister caused by the change in transportation speed of the web paper may possibly remain. Especially, the printer with high resolution may possess a drawback that extremely minute residue of the misregister causes degraded printing quality.